Pragmatic trials were first proposed by Schwartz and Lellouch in 1967 as trials performed under normal conditions with the intention of providing results that are more applicable to clinical practice and decision making. The alternative, taking a more explanatory approach, leads to tightly controlled trials under ideal conditions that aim to provide understanding of how treatments work. Explanatory trials have an important role but healthcare interventions are seldom given under circumstances similar to those used in such trials.

Many authors have highlighted the need for trials with greater applicability (Rothwell 2005, Treweek 2009) in other words, trials that pay attention to external validity as well as internal validity. Lack of consideration of external validity is the most frequent criticism by clinicians of RCTs, systematic reviews, and guidelines (Rothwell 2005).

Trial teams can use PRECIS-2 to guide discussion on how explanatory or pragmatic they wish their trials to be and to guide decision making on the design of trial domains. We believe PRECIS-2 enables trialists to consider how applicable their trial results will be in the “real world”.